Dual motor question

["Peter VanDerWal" <peter_v@primenet.com>]

    After watching the dual motor cars at the Woodburn drags I've been
trying to figure out the advantages of this setup.

Please note: I'm not knocking this setup, I was very impresses with the
performance of both the cars I saw (Dueling Sevens and the scratch built one
that one of the guys at work thought was a golf cart on steroids after
watching it on ESPN.  )

    At first I thought you would get twice the power, but I believe both of
the cars only used one controller so that's no the case.

    I don't know how the dueling sevens is setup so I'll just state what I
know about the scratch built car (sorry but I can't remember it's name or
the names of the fellows that built it).

    The scratch built had dual ADC motors setup so the could be wired in
series or parallel and fed by a single controller.  The idea was to be able
to eliminate a transmission. It seems to me that for the cost of a second
motor you could buy a rebuilt tranny for a scratch built and if you are
converting you probably already have one.

    I've been looking at the motor charts for the prestolite motor since I
don't have any for ADC motors, I'm going to assume that most/all series
motors are going to act in a similar manner.  The following is what I've
been able to determine from looking at the charts,  and of course I realize
this isn't as accurate as real world testing.

    I'm going to assume a simple two speed transmission with second gear
having 1/2 the reduction of first gear.  This way the single motor in first
gear will act like the dual motors in series and second gear is like the
duals in parallel.
    Also from previous posts I know that a tranny is about 90% efficient,
but I'm pretty sure that at least 1/2 the losses are in the differential.
Since you still need the differential in the dual motor setup, this means
that the tranny setup only has about 5% more transmission losses that the
dual motor setup.
    However; the dual motor setup is about 10% less efficient at both low
rpms (high current) and high rpms (twice the friction, fan, and windage
losses) so this means the tranny setup has about a 5% advantage.

    At low speeds in first gear the single motor will be turning twice as
fast so it's internal fans will cool it better.  This would indicate it
would be better for climbing long hills.
    Also since we only need two speeds you could remove the rest of the
gears and their syncros and thereby increase the efficiency advantage of the
single motor setup.
    Also the tranny setup seems to me to be cheaper since a tranny costs
about the same as a motor or even less if you get one from a junk yard.
Also the dual motor setup needs a bunch of expensive contactors to handle
the series parallel setup and motor reversing.

    Again I'm not trying to knock the dual motor setup, I just don't see the
advantage to it.

P.S. the guys a work saw the drags on EPSN and were talking about them when
I got to work. They were real impressed with how handily the scratch built
beat the RX7 (dueling sevens?), especially with the late start it got.
Unfortunately I missed seeing it on TV :-(